Posts Tagged ‘Evolution of Feathers and Flight’

A very exciting fossil was just recently found and reported (the journal citation is below)!  Near Grassy Lake in southwestern Alberta, Canada, an ostrich-like ornithomimid has been found that had feathers!  This is the first time a feathered dinosaur has been found anywhere in the western hemisphere.  Fossils of three individuals were found that have the definite impressions of feathers on their bodies.  One was a juvenile animal that seems to have been covered with a fine layer of feathers similar to the down of modern birds.  The other two individuals were both adults.  These ornithomimids have the same downy covering as the juvenile on their bodies, but they also had much larger and longer fealthers on their forelimbs.  These larger feathers have many similarities in structure to the wing feathers of modern birds.  However, these ornithomimids had far to few feathers to fly, and they were far to big to ever be able to get off the ground even if they did have full feathered wings.  This reenforces the idea that feathers first evolved in reponse to a selection pressure other than to fly.

Thurmoregulation has become a front runner in the driving force for feather evolution.  Small animals have a lot of surface area in comparision to their body volume and so tend to loose heat very rapidly when compared to larger animals.  It is not surprising then that most of the feathered dinosaurs that have been found have been small.  Even the largest known feathered dinosaur, Yutyrannus huali, which was a relative of Tyrannosaurus rex,  fits with this pattern since it lived at a time of cimatic cooling.

The presents of the larger feathers on the adult ornithomimids, but not the juvenile, suggests another use.  Wing feathers on modern birds develop very early, with the flight feathers being some the very first fethers adult to grow on a baby bird.  The reversal of this order in the ornithomids found in Alberta suggests that they may have had some function that was only important in adulthood such as signaling or incubation.  I personally find the signaling hypothesis to be the most interesting.  We know that many of the feathered dinosaurs had feathers of a range of colors from white to black to grey to brown to red, so the idea that these colored feathers could have functioned in the same ways that colored feathers do today in birds (territorial displays, mate attraction, etc.) does not seem like a far leap.  it also begins to give a glimps into dinosaur behavior which opens the door to all kinds of questions.

Another aspect of this new find that is exciting is that it was found in sandstone.  Pretty much all the other feathered fossils have been found in very fine shales.  However, sandstone is where most fossils are found.  So finding feathers fossilized in sandstone gives paleontologists hope that many more such fossils may be found then had previously been thought possible.


D. K. Zelenitsky, F. Therrien, G. M. Erickson, C. L. DeBuhr, Y. Kobayashi, D. A. Eberth, F. Hadfield. Feathered Non-Avian Dinosaurs from North America Provide Insight into Wing Origins. Science, 2012; 338 (6106): 510 DOI: 10.1126/science.1225376

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